Often, in carrying out metallurgical operations, fluids are passed into the molten metal contained within a metallurgical vessel from below the molten metal surface. Examples of such injection operations include the passage of gas into molten metal to flush out impurities, the passage of gas into molten metal to stir or otherwise agitate the melt, and the passage of gas into molten metal for reaction with melt constituents.
One means by which fluids are passed into the molten metal is through one or more tuyeres which pass through the wall of the metallurgical vessel and which are connected at one end with a source of gas or gases and which at the other end communicate with the vessel interior. Generally the vessel walls are lined with refractory material and the tuyeres pass through and are in contact with this refractory for a portion of their length.
The tuyeres operate under severe conditions, especially at their injection end which contacts the molten metal. For example, the temperature of molten steel generally exceeds about 2500.degree. F. These severe conditions cause the tuyere to wear and eventually to require replacement. The wear occurs at the injection end or tip of the tuyere. It is of course desirable to have a tuyere which will wear more slowly than presently available tuyeres.
When gas injection is used for flushing or stirring, the gas or gases generally employed are inert to the molten metal. However, when a reaction such as decarburization is carried out, the wear problem is more severe because the reactions being carried out at the tuyere tip are generally exothermic. For example, decarburization is usually carried out by the injection of oxygen or oxygen and inert gas into the melt. The very high temperatures caused by the reaction of melt constituents with, for example, oxygen, combined with the vigorous localized agitation caused by the gas injection and reaction, cause extremely severe wear at the tuyere tip when reactive gas injection is carried out.
Those skilled in the art have addressed the problem of severe tuyere wear, especially when a reactive gas is injected, and have devised the annular tuyere directed to the problems. The annular tuyere comprises a central conduit and an annular conduit around and along the central conduit. Such a tuyere most often comprises inner and outer concentric tubes. Reactive gas, such as oxygen, is passed into the melt through the central conduit and an inert gas or liquid, such as argon, nitrogen or a hydrocarbon is passed into the melt through the annular and central passages. The shroud gas serves to shield the tuyere tip from some of the more severe effects of the gas injection and thus to prolong the life of the tuyere by causing it to wear at a slower rate.
A problem which has been observed with annular tuyeres is the tendency of the outer conduit to wear at a faster rate than that of the inner conduit. This reduces to some extent the beneficial wear resistant aspects of the annular tuyere because the wear of the inner conduit is controlled by the wear of the outer conduit. This problem may be addressed by providing yet another annulus around the first annulus, but this solution is costly and is still unsatisfactory since the outermost conduit still exhibits higher wear than the inner conduits.
Accordingly it is an object of this invention to provide a tuyere which exhibits greater wear resistance at the tip than that possible with heretofore available tuyeres.
It is a further object of this invention to provide on annular tuyere which exhibits greater wear resistance at the tip than that possible with heretofore available annular tuyeres.
It is another object of this invention to provide a metallurgical vessel having at least one tuyere which exhibits greater wear resistance at the tip than that possible with heretofore available tuyeres.